This application is based on Application No. 2001-141655, filed in Japan on May 11, 2001, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a radar apparatus mounted on a moving body such as a vehicle, and more particularly, to a radar signal processing apparatus capable of detecting an object as a target of measurement with a radar to measure a relative distance and a relative speed between the target and the radar (hereinafter referred to as xe2x80x9crelative distancexe2x80x9d or xe2x80x9cthe distancexe2x80x9d and xe2x80x9crelative speedxe2x80x9d or xe2x80x9cthe speedxe2x80x9d, respectively). Further the present invention relates to a method of measuring the distance and the speed with the radar signal processing apparatus.
2. Description of the Related Art
Radar apparatuses mounted on vehicles or the like only covers a range of about several to several hundreds of meters in which the radar apparatuses can measure the distances to the targets. It is desirable for the radar apparatuses with such a range to have a transmitting antenna and a receiving antenna combined into one in terms of reduction in size if mounted on the vehicles or the like. As a conventional radar apparatus designed to meet such a requirement, a frequency modulated interrupted continuous wave (FMICW) radar apparatus is known.
The conventional radar apparatus will be described with reference to drawings.
FIG. 10 is a block diagram showing the basic structure of a transmitter/receiver 1 of an FMICW radar apparatus.
Referring to FIG. 10, the radar transmitter/receiver 1 has a transmission/reception control section 2, a modulated waveform generation section 3, a voltage controlled oscillator (VCO) 4, a first switch 5, a second switch 6, an antenna 7, distribution circuits 9a and 9b, a phase shift circuit 10, and mixers 11a and 11b. A target to be detected by the radar apparatus is indicated by 8 in FIG. 10.
FIG. 11 is a diagram showing the structure of a radar signal processing apparatus 12 to which a received signal and a control signal of FIG. 10 are input.
Referring to FIG. 11, the radar signal processing apparatus 12 has a signal processing control section 13, a third switch 14, analog to digital converters (ADCs) 15a and 15b, memories 16a and 16b, range gates 17a and 17b, frequency extraction sections 18a and 18b, and a distance and speed derivation section 19.
The operation of the conventional radar apparatus will be described with reference to drawings.
FIG. 12 is a diagram showing the frequencies of signals with respect to time in the FMICW radar apparatus. In the following description, a state of modulation in a period where the frequency increases with time is referred to as xe2x80x9cup phasexe2x80x9d and a state of modulation in a period where the frequency decreases with time is referred to as xe2x80x9cdown phasexe2x80x9d.
FIG. 12 shows an up-phase VCO signal 20a, a down-phase VCO signal 20b, an up-phase signal 21a to be transmitted, a down-phase signal 21b to be transmitted, an up-phase local signal 22a, a down-phase local signal 22b, an up-phase received signal 23a, a down-phase received signal 23b, an up-phase beat signal 24a, and a down-phase beat signal 24b. 
FIG. 13 is a diagram showing connection to a contact with respect to time in each of the first and second switches 5 and 6 shown in FIG. 10.
FIG. 14 is a diagram showing a data matrix formed in each of the memories 16a and 16b shown in FIG. 11 by sampling up-phase or down-phase beat signals.
FIG. 15 is a flowchart showing the procedure of signal processing in the radar signal processing apparatus shown in FIG. 11.
The operation of the FMICW radar apparatus will be described. The FMICW radar apparatus intermittently uses a frequency modulated continuous wave as its name implies.
Referring to FIG. 10, a modulated waveform which has up and down phases and which is generated by the modulated waveform generation section 3 is input to the VCO 4 through a control of the transmission/reception control section 2 in the radar transmitter/receiver 1, and a VCO signal 20 shown in FIG. 12 is formed from the input by the VCO 4 and is input to the first switch 5.
The first switch 5 and the second switch 6 are controlled by the transmission/reception control section 2 so as to repeat establishing synchronized connection through a contact t during a time period xcfx84 set in advance and connection through a contact r during another time period Txe2x88x92xcfx84, as shown in FIG. 13.
During the up-phase period, the VCO signal 20a is fed through the contact t for the time period xcfx84 to produce a wave of a signal 21a to be transmitted. The signal 21a is supplied to the antenna 7 through the first switch 5 and the second switch 6 to radiate from the antenna 7 into air.
The transmitted signal 21a radiating into air is applied to the target 8 which is moving at a certain relative speed V while keeping a certain relative distance R, and part of the signal is reflected by the target 8. The reflected wave from the target 8 is shifted by a Doppler frequency Fv according to the relative speed V and is received as the received signal 23a shown in FIG. 12 by the antenna 7 with a delay of Kxcfx84=2R/c (c: the speed of electric waves) from the time at which the signal 21a is transmitted. The received signal 23a is input to the distribution circuit 9a via the second switch 6 in which connection through the contact r is made for the time period Txe2x88x92xcfx84. The distribution circuit 9a divides the input signal into two signals which are respectively input to the mixers 11a and 11b. 
On the other hand, the VCO signal 20a fed through the first switch 5 in which connection through the contact r is made for the time period Txe2x88x92xcfx84 is input as the local signal 22a to the distribution circuit 9b. The distribution circuit 9b divides the input signal into two signals which are respectively input to the mixer 11a and the phase shift circuit 10.
The phase shift circuit 10 shifts the phase of the input signal by xcfx80/2 radian and outputs the phase shifted signal to the mixer 11b. 
The received signal 23a and the local signal 22a respectively input to the mixers 11a and 11b are mixed in a period Kxcfx84 to (K+1)xcfx84 in the time period Txe2x88x92xcfx84 to form the beat signal 24a in which the frequency difference between the received signal 23a and the local signal 22 appears as a frequency.
At this time, the beat signal 24a is obtained as a complex signal from the mixers 11a and 11b, the beat signal 24a from the mixer 11a corresponding to the real part (I) of the complex signal, the beat signal 24a from the mixer 11b corresponding to the imaginary part (Q) of the complex signal.
During the down-phase period, the beat signal 24b is obtained in the same manner as during the up-phase period.
The beat signals 24a in the up-phase is represented by Sup(t) in an equation (1) shown below and the beat signal 24b in the down-phase is represented by Sdn(t) in an equation (2) shown below.
Sup(t)=Aupxc2x7exp(j2xcfx80Uxc2x7t+xcfx86up)=Aupxc2x7cos(2xcfx80Uxc2x7t+xcfx86up)+jAupxc2x7sin(2xcfx80Uxc2x7t+xcfx86up)xe2x80x83xe2x80x83(1)
Sdn(t)=Adnxc2x7exp(j2xcfx80Dxc2x7t+xcfx86dn)=Adnxc2x7cos(2xcfx80Dxc2x7t+xcfx86dn)+jAdnxc2x7sin(2xcfx80Dxc2x7t+xcfx86dn)xe2x80x83xe2x80x83(2)
                    U        =                                            -                                                2                  ⁢                  B                                                  c                  ⁢                                      xe2x80x83                                    ⁢                  T                                                      ⁢            R                    +                                    2              λ                        ⁢            V                                              (        3        )                                D        =                                                            2                ⁢                B                                            c                ⁢                                  xe2x80x83                                ⁢                T                                      ⁢            R                    +                                    2              λ                        ⁢            V                                              (        4        )            
(Aup, Adn: amplitude terms; xcfx86up, xcfx86dn: phase terms; U: up-phase beat frequency; D: down-phase beat frequency; B: frequency sweep width; T: frequency sweep time; c: speed of light; xcex: wavelength; R: relative distance to target; and V: relative speed of target)
Beat signals (I and Q) and a control signal (x) from the transmission/reception control section 2 are supplied from the radar transmitter/receiver 1 to the radar signal processing apparatus 12.
On the basis of the control signal from the transmission/reception control section 2, the signal processing control section 13 of the radar signal processing apparatus 12 makes connection through a contact U in the third switch 14 during the up-phase period and makes connection through a contact D in the third switch 14 during the down-phase period.
This switching enables the up-phase beat signal to be sampled by the ADC 15a during every period xcfx84 in the time period xcfx84 to T to be stored in the memory 16a, and also enables the down-phase beat signal to be sampled by the ADC 15b during every period xcfx84 in the time period xcfx84 to T to be stored in the memory 16b. 
Of either beat signal, when stored, N samples {P(1), R(1)}, {P(1), R(2)}, {P(1), R(3)}, . . . {P(1), R(N)} from P(1) which is transmitted the signal 21a or 21b are stored in order by the signal processing control section 13, as shown in FIG. 14.
Similarly, samples from (P2), i.e., {P(2), R(1)}, {P(2), R(2)}, {P(2), R(3)}, . . . {P(2), R(N)}, are also stored, thus forming a data matrix with respect to each phase. In the matrix, the row R(k) (k=1 to N) includes the signal of the target at the relative distance in the range expressed by the following equation (5).                               k          ⁢                      xe2x80x83                    ⁢                                    c              ⁢                              xe2x80x83                            ⁢              τ                        2                           less than                   R          ⁢                      xe2x80x83                    ⁢          k                ≤                              (                          k              +              1                        )                    ⁢                                    c              ⁢                              xe2x80x83                            ⁢              τ                        2                                              (        5        )            
On the basis of the control signal from the transmission/reception control section 2, the signal processing control section 13 determines the time at which sampling of the final transmitted signal P(M) is completed, and proceeds to perform the next signal processing. The operation of the radar apparatus will be described with respect to details of the next signal processing with reference to FIG. 15.
In the first step ST1 of the procedure shown in FIG. 15, the signal processing control section 13 sets a range gate number counter (internal variable) k provided in itself to k=1.
In step ST2, the signal processing control section 13 controls the range gate 17a so that connection through the k-th contact is made. The k-th range gate data sequence in an up phase {P(1), R(k)}, {P(2), R(k)}, . . . {P(M), R(k)} is extracted from the memory 16a through this connection in the range gate 17a and is input to the frequency extraction section 18a. The frequency extraction section 18a performs frequency analysis on this range gate data sequence, for example, by fast Fourier transform (FFT) and sends a beat frequency extraction result corresponding to the target to the signal processing control section 13.
In step ST3, the signal processing control section 13 receives the extraction result from the frequency extraction section 18a and makes a determination as to whether a beat frequency has been extracted. If a beat frequency has been extracted, the process advances to step ST4. If no beat frequency has been extracted, the process moves to step ST7.
In step ST4, the signal processing control section 13 controls the range gate 17b so that connection through the k-th contact is made, as in step ST2. The k-th range gate data sequence in a down phase {P(1), R(k)}, {P(2), R(k)}, . . . {P(M), R(k)} is extracted from the memory 16b through this connection in the range gate 17b and is input to the frequency extraction section 18b. The frequency extraction section 18b performs frequency analysis on this range gate data sequence, for example, by FFT and sends a beat frequency extraction result corresponding to the target to the signal processing control section 13.
In step ST5, the signal processing control section 13 receives the extraction result from the frequency extraction section 18b and makes a determination as to whether a beat frequency has been extracted. If a beat frequency has been extracted, the process advances to step ST6. If no beat frequency has been extracted, the process moves to step ST7.
In step ST6, the distance and speed derivation section 19 forms all combinations of extracted beat frequencies U1, U2, . . . AUp in the up phase and beat frequencies D1, D2, . . . ADq in the down phase, and searches for a pair of frequencies Cij (Ui, Dj) at which the relative distance R obtained by an equation (6) shown below is within the range Rk expressed by equation (5). If a pair of frequencies which meet the condition is found, the relative speed V of the target is obtained by using an equation (7) shown below.                     R        =                                            c              ⁢                              xe2x80x83                            ⁢              T                                      4              ⁢              B                                ⁢                      (                          D              -              U                        )                                              (        6        )                                V        =                              λ            4                    ⁢                      (                          U              +              D                        )                                              (        7        )            
In step ST7, the signal processing control section 13 compares the value of the counter k with N. If k is not equal to N, the process advances to step ST8. If k is equal to N, the process moves to step ST9.
In step ST8, the signal processing control section 13 increments the value of the counter k. The process then moves to step ST2.
In step ST9, the signal processing control section 13 makes a decision on termination of the operation. If the decision is not to terminate the operation, the process returns to step ST1. If the decision is to terminate the operation, the operation is terminated. For example, the operation is terminated when an instruction from an operator is input to the signal processing control section 13.
In the conventional FMICW radar apparatus arranged as described above, frequency extraction from all the N distance bins must be performed with respect to each phase and it is not always possible to perform extraction processing in real time.
Japanese Patent Application Laid-open No. 2000-275333 discloses, as means for solving this problem, a method of adding a plurality of different range gate data sequences to reduce the number of range gate data groups to be processed.
FIG. 16 shows the structure of another conventional radar signal processing apparatus arranged to realize this solution.
The processor shown in FIG. 16 has an addition range gate setting section 25 and plural range gate addition sections 26a and 26b. 
FIG. 17 is a flowchart showing the procedure of signal processing in this conventional radar signal processing apparatus.
The operation of the FMICW radar apparatus will be described. The operation is performed in the same manner as that of the above-described conventional FMICW radar apparatus with respect to the procedure up to the process of forming a data matrix by storing up-phase and down-phase beat signals in the memories 16a and 16b, respectively.
In the first step ST1 shown in FIG. 17, the signal processing control section 13 sets a range gate number counter k provided in itself to k=1.
In step ST10, the signal processing control section 13 notifies the addition range gate setting section 25 of the completion of sampling of the final transmitted signal P(M) and the addition range gate setting section 25 receiving this notice outputs to the plural range gate data addition section 26a range gate numbers designating data to be combined by arithmetic addition. For example, when the i-th range gate data and the (i+j)th range gate data are added together, the plural range gate data addition section 26a performs arithmetic addition of up-phase data as expressed by {P(1), R(i)}+{P(1), R(i+j)}, {P(2), R(i)}+{P(2), R(i+j)}, . . . , {P(m), R(i)}+{P(m), R(i+j)} and, from this result, newly forms a data sequence {P(1), RR(h)}, {P(2), RR(h)}, . . . , {P(m), RR(h)}.
In step ST11, the frequency extraction section 18a performs frequency analysis, for example, by FFT on the new data sequence formed in step ST9 and sends a beat frequency extraction result corresponding to the target to the signal processing control section 13.
In step ST3, the signal processing control section 13 receives the extraction result from the frequency extraction section 18a and makes a determination as to whether a beat frequency has been extracted. If a beat frequency has been extracted, the process advances to step ST12. If no beat frequency has been extracted, the process moves to step ST14.
In step ST12, the addition range gate setting section 25 outputs to the plural range gate data addition section 26b range gate numbers designating data to be combined by arithmetic addition, as it does in step ST10. For example, when the i-th range gate data and the (i+j)-th range gate data are added together, the plural range gate data addition section 26b performs arithmetic addition of down-phase data as expressed by {P(1), R(i)}+{P(1), R(i+j)}, {P(2), R(i)}+{P(2), R(i+j)}, . . . , {P(m), R(i)}+{P(m), R(i+j)} and, from this result, newly forms a data sequence {P(1), RR(h)}, {P(2), RR(h)}, . . . , {P(m), RR(h)}.
In step ST13, processing similar to that in step S11 is performed, that is, the frequency extraction section 18b performs frequency analysis, for example, by FFT on the new data sequence formed in step ST12 and sends a beat frequency extraction result corresponding to the target to the signal processing control section 13.
In step ST5 the signal processing control section 13 receives the extraction result from the frequency extraction section 18b and makes a determination as to whether a beat frequency has been extracted. If a beat frequency has been extracted, the process advances to step ST6. If no beat frequency has been extracted, the process moves to step ST14.
In step ST6, the relative distance and the relative speed of the target are obtained in the same manner as in the above-described well-known FMICW radar apparatus.
In step S14, the signal processing control section 13 compares the value of the counter k with H (=N/2). If k is not equal to H, the process advances to step ST8. If k is equal to H, the process moves to step ST9.
In step ST8, the signal processing control section 13 increments the value of the counter k. The process then moves to step ST10.
In step ST9, the signal processing control section 13 makes a decision on termination of the operation. If the decision is not to terminate the operation, the process returns to step ST1. If the decision is to terminate the operation, the operation is terminated. For example, the operation is terminated when an instruction from an operator is input to the signal processing control section 13.
In the conventional FMICW radar apparatus arranged as described above, there is a possibility that beat frequencies existing in different range gates and corresponding to a different target may be erroneously selected as a frequency pair to generate the distance and speed of a target which cannot exist actually, so that the reliability of measurement results is reduced.
In view of the above-described problem, an object of the present invention is to provide a radar signal processing apparatus in which signal processing of a smaller amount of data is ordinarily performed and high-load accurate signal processing is performed only on a range gate data sequence with a strong possibility of existence of a target, and which can perform real-time signal processing in this manner without reducing the reliability of measurement results.
A radar signal processing apparatus according to a first aspect of the present invention has a memory in which a beat signal sampled at predetermined time intervals is stored, a range gate for extracting a range gate data sequence from the memory, a first frequency extraction section which extracts a beat frequency corresponding to a target by performing frequency analysis by FFT at a low computation load and with low frequency measurement accuracy on all range gate data sequences extracted by the range gate, a second frequency extraction section which extracts a beat frequency corresponding to the target by performing frequency analysis by FFT at a high computation load and with high frequency measurement accuracy only on the range gate data sequence from which a beat frequency has been extracted by the first frequency extraction section, and a distance and speed derivation section which obtains a relative distance and a relative speed of the target on the basis of the beat frequency extracted by the second frequency extraction section. That is, signal processing of a smaller amount of data is ordinarily performed and high-load accurate signal processing is performed only on a range gate data sequence with a strong possibility of existence of a target, thus enabling real-time processing without reducing the reliability of measurement results.
A radar signal processing apparatus according to a fourth aspect of the present invention has a memory in which a beat signal sampled at predetermined time intervals is stored, a range gate for extracting a range gate data sequence from the memory, a range gate prediction section which predicts the relative distance of a target at the next observation time from the relative distance and the relative speed of the target derived at the current observation time, and which obtains a range gate data sequence corresponding to the predicted distance, a first frequency extraction section which extracts a beat frequency corresponding to a target by performing frequency analysis by FFT at a low computation load and with low frequency measurement accuracy on the range gate data sequence extracted by the range gate if the range gate data sequence which is the object to be processed does not coincide with the range gate data sequence predicted by the range gate prediction section, a second frequency extraction section which extracts a beat frequency corresponding to the target by performing frequency analysis by FFT at a high computation load and with high frequency measurement accuracy on the range gate data sequence extracted by the range gate if the range gate data sequence which is the object to be processed coincides with the range gate data sequence predicted by the range gate prediction section, and a distance and speed derivation section which obtains the relative distance and the relative speed of the target on the basis of the beat frequency extracted by the first or second frequency extraction section. That is, signal processing of a smaller amount of data is ordinarily performed and high-load accurate signal processing is performed only on a range gate data sequence with a strong possibility of existence of a target, thus enabling real-time processing without reducing the reliability of measurement results.
A radar signal processing apparatus according to a sixth aspect of the present invention has a memory in which a beat signal sampled at predetermined time intervals is stored, a range gate for extracting a range gate data sequence from the memory, a range gate prediction section which predicts the relative distance of a target at the next observation time from the relative distance and the relative speed of the target derived at the current observation time, and which obtains a range gate data sequence corresponding to the predicted distance, a first frequency extraction section which extracts a beat frequency corresponding to a target by performing frequency analysis by FFT at a low computation load and with low frequency measurement accuracy on all the range gate data sequences extracted by the range gate if the range gate data sequence which is the object to be processed does not coincide with the range gate data sequence predicted by the range gate prediction section, a second frequency extraction section which extracts a beat frequency corresponding to the target by performing frequency analysis by FFT at a high computation load and with high frequency measurement accuracy only on the range gate data sequence from which a beat frequency has been extracted by the first frequency extraction section if the range gate data sequence which is the object to be processed does not coincide with the range gate data sequence predicted by the range gate prediction section, and which extracts a beat frequency corresponding to the target by performing frequency analysis by FFT at a high computation load and with high frequency measurement accuracy on the range gate data sequence extracted by the range gate if the range gate data sequence which is the object to be processed coincides with the range gate data sequence predicted by the range gate prediction section, and a distance and speed derivation section which obtains the relative distance and the relative speed of the target on the basis of the beat frequency extracted by the second frequency extraction section. That is, signal processing of a smaller amount of data is ordinarily performed and high-load accurate signal processing is performed only on a range gate data sequence with a strong possibility of existence of a target, thus enabling real-time processing without reducing the reliability of measurement results.
A method of measuring a distance and a speed using FMICW according to an eighth aspect of the present invention, includes the steps of: extracting a first beat frequency corresponding to a target by performing frequency analysis by FFT at a low computation load and with low frequency measurement accuracy on all range gate data sequences extracted from a memory by a range gate; extracting a second beat frequency corresponding to the target by performing frequency analysis by FFT at a high computation load and with high frequency measurement accuracy only on the range gate data sequence from which the first beat frequency has been extracted; and obtaining the relative distance and the relative speed of the target on the basis of the second beat frequency extracted. That is, signal processing of a smaller amount of data is ordinarily performed and high-load accurate signal processing is performed only on a range gate data sequence with a strong possibility of existence of a target, thus enabling real-time processing without reducing the reliability of measurement results.
A method of measuring a distance and a speed using FMICW according to a ninth aspect of the present invention includes: the steps of predicting the relative distance of a target at the next observation time from the relative distance and the relative speed of the target derived at the current observation time to obtain a range gate data sequence corresponding to the predicted distance; extracting a first beat frequency corresponding to a target by performing frequency analysis by FFT at a low computation load and with low frequency measurement accuracy on a range gate data sequence extracted by the range gate if the range gate data sequence which is the object to be processed does not coincide with the predicted range gate data sequence; extracting a second beat frequency corresponding to the target by performing frequency analysis by FFT at a high computation load and with high frequency measurement accuracy on the range gate data sequence extracted by the range gate if the range gate data sequence which is the object to be processed coincides with the predicted range gate data sequence; and obtaining the relative distance and the relative speed of the target on the basis of the extracted first or second beat frequency. That is, processing of a smaller amount of data is ordinarily performed and high-load accurate signal processing is performed only on a range gate data sequence with a strong possibility of existence of a target, thus enabling real-time processing without reducing the reliability of measurement results.
A method of measuring a distance and a speed using FMICW according to a tenth aspect of the present invention, includes the steps of: predicting the relative distance of a target at the next observation time from the relative distance and the relative speed of the target derived at the current observation time to obtain a range gate data sequence corresponding to the predicted distance; extracting a first beat frequency corresponding to a target by performing frequency analysis by FFT at a low computation load and with low frequency measurement accuracy on all the range gate data sequences extracted by the range gate if the range gate data sequence which is the object to be processed does not coincide with the predicted range gate data sequence; extracting a second beat frequency corresponding to the target by performing frequency analysis by FFT at a high computation load and with high frequency measurement accuracy only on the range gate data sequence from which the first beat frequency has been extracted if the range gate data sequence which is the object to be processed does not coincide with the range gate data sequence predicted by the range gate prediction section, and extracting a second beat frequency corresponding to the target by performing frequency analysis by FFT at a high computation load and with high frequency measurement accuracy on the range gate data sequence extracted by the range gate if the range gate data sequence which is the object to be processed coincides with the predicted range gate data sequence; and obtaining the relative distance and the relative speed of the target on the basis of the second beat frequency extracted. That is, processing of a smaller amount of data is ordinarily performed and high-load accurate signal processing is performed only on a range gate data sequence with a strong possibility of existence of a target, thus enabling real-time processing without reducing the reliability of measurement results.